Had same problem a couple of years ago. Used vice grips and massage vibrator to remove key. Ordered new tumbler from MB and drove happily for two years. Then suddenly key stuck again. Vice grips and vibrator again. This time I was pretty sure that the problem was not tumbler, but rather column locking mechanism. A machinist friend helped me (or actually I watched him) fit a metal spacer in the switch that jammed the column lock into the open position. Now the steering wheel does not lock, which is of no concern to me, but the buzzer sounds off if the driver's door is open - even without the key in the ignition. A small price to pay, compared to the amount of work it saved.

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln